1. Field of the Invention
The present invention relates generally to a method for synthesizig epoxysilicone and allyl-terminated silicone compounds. More particularly, the present invention relates to a method for synthesizing epoxysilicone and allyl-terminated silicone compounds which have improved toughness, moisture stability, and thermal stability.
2. Description of the Background Art
Epoxy resins are widely used as adhesives, encapsulants, and coatings for a variety of applications. In particular, for application to structural and electronic devices and circuits, epoxy resins are useful since they provide mechanical protection, thermal and oxidation stability, good substrate adhesion, and moisture and solvent resistance. However, a problem common to the myriad of epoxy systems is the development of thermomechanical stresses and strains when the encapsulated devices, bonded assemblies, or coated substrates are heated or cooled. While the use of flexibilized epoxies can result in minimizing this thermal-mechanical cycling problem, such systems generally possess poor thermal stabilities. Another important property of an adhesive coating or encapsulant is its repairability. As expected, rigid systems are generally significantly more difficult to repair or replace then ductile ones.
One group of epoxy resins particularly useful for electronic applications consists of epoxysilicone compounds, which are compounds comprising silicon atoms joined together by oxygen linkages and further comprising terminal glycidyl groups. Such epoxysilicone compounds have been known for many years and are described in the publications by Bilow, Lawrence, and Patterson, "Synthesis and Polymerization of 1,3-bis-(2,3-epoxypropylphenyl)-tetramethylsiloxanes and Related Compounds," Journal of Polymer Science, Vol. 5, 1967, pages 2595-2615 and by Patterson and Bilow, "Polymers from Siloxane-Containing Epoxides," Journal of Polymer Science, Vol. 7, 1969, pages 1089-1110. As described in these references, such epoxysiloxane compounds were prepared by reacting the Grignard reagent derivable from an allylbromobenzene with a large excess of dimethyldichlorosilane. The resulting compound, chlorodimethyl(allylphenyl)silane, must be isolated from excess dichlorodimethylsilane by repeated distillation steps. Chlorodimethyl(allylphenyl)silane was then hydrolyzed to give 1,3-bis(allylphenyl)-1,1,3,3-tetramethyl-1,3-disiloxane. Epoxidation was effected either with 3-chloroperoxybenzoic acid or trifluoroperoxyacetic acid. However, such a procedure is not only tedious, but also yields a product contaminated by impurities produced by rearrangement or reversion in which --Si--O-- groups break away from the rest of the molecule and form macrocycles or higher linear chains. In addition, the corrosive trifluoroperoxyacetic acid was difficult and dangerous to prepare on a large scale and the 3-chlorobenzoic acid side product generated in the epoxidation reaction was so soluble with the desired product that complete removal of this acid residue was impossible. Furthermore, such a process is not conducive to tailor making the length of the siloxane chain.
Thus, a need exists for a method of synthesizing high purity epoxysilicone compounds which form resins that exhibit toughness, repairability, thermal and oxidative stability, and moisture and solvent resistance. In addition, a need exists for a method of synthesizing the allyl compounds from which such epoxy resins, among others, may be formed.